The present invention relates to a non-aqueous electrolyte cell comprising an electrode assembly including an anode in the form of a belt consisting essentially of a consumable light metal such as lithium, a cathode in the form of a belt and a separator interposed between the anode and the cathode. The anode, the separator and the cathode are spirally wound so that the anode is positioned on the outer side of the cathode. More specifically, the present invention relates to a non-aqueous electrolyte cell in which an anode collector is disconnected from the anode light metal remaining in the outermost spiral of the electrode assembly at the last stage of discharge.
Non-aqueous electrolyte cells using a consumable light metal such as lithium as the anode active material and using oxide or the like as the cathode active material has various advantages hardly seen in other primary cells; for example, such cells have a high voltage, a high energy density, small self discharge and remarkably long shelf life. Consequently, such cells have -a rapidly growing demand in recent years and have been applied to a variety of electronic devices.
Non-aqueous electrolyte cells of this kind generally comprise an electrode assembly including an anode strip in the form of a belt, a cathode strip in the form of a belt and a separator interposed therebetween. The anode, the separator and the cathode are spirally wound so that the anode is positioned on the outer side of the cathode. The section of the anode positioned in the outermost spiral of the spirally wound electrode assembly has only its inner side facing the cathode, therefore such section of the anode has smaller rate of consumption compared to the inner section of the anode, sandwiched by the cathode on both sides. In a construction where the anode current collector is disposed in the outermost spiral of the spirally wound electrode assembly and the outermost end of the anode is positioned slightly further than that of the cathode in the winding direction, discharge capacity making good use of the anode light metal can be obtained. In such a construction, however, an active light metal remains in electrical contact with the anode current collector even when the cell is in the last stage of discharge.
When the cell in such a state is forcedly discharged or subjected to voltage reversal by being connected in series with a cell with small discharge amount or with a new cell, the light metal in the anode dissolves and electrolytically plates onto the cathode. If such forced discharge continues, the light metal electrolytically plating onto the cathode breaks through the separator to cause an internal short circuit. If an internal short circuit occurs, a tremendous amount of current surges through the internal short circuit section, causing a rapid rise in temperature. Further, if sparks generate inside the cell filled with gas at an internal short circuit, the sparks might become an ignition source and might ignite the cell.
In order to avoid the above-described inconveniences, as shown in FIG. 10, it has been proposed to dispose an anode current collector 96 at one revolution or further inward from an outermost end 93a of an anode 93, that is, at the winding beginning side, and to constitute so that an outermost end 92a of a cathode 92 reacts only with the anode on its inner side of spiral. With this construction, as shown in FIG. 11, an anode metal 93b remaining in the outermost spiral is disconnected from the current collector 96 at the last stage of discharge (disclosed in Japanese Laid-Open Patent Publication Hei 5-13089).
Nevertheless, for practical use, when producing an electrode assembly by laying one on top of another the cathode, the anode and the separator, each being in the form of a belt, and spirally winding these cathode, anode and separator by means of an automatic winding apparatus, it is very difficult to secure a cathode section that is not in opposition to the anode on the outer spiral by positioning the outermost end of the anode so that the outermost end of the cathode reacts only with the anode on its inner side.
Further, disconnecting the anode metal in the outermost spiral from the anode current collector at the last stage of discharge by positioning the anode current collector at one revolution or further inward from the outermost end of the anode means rendering the use of the cell impossible although the anode active material capable of discharging remains and leads to a decrease in discharge capacity.
The present invention aims at solving the above-described inconveniences with the conventional non-aqueous electrolyte cells.
It is an object of the present invention to provide a non-aqueous electrolyte cell ensuring disconnection of remaining non-reacted anode active material from the anode current collector when forcedly discharged at the last stage of discharge and having an improved discharge capacity.
A non-aqueous electrolyte cell according to the present invention comprises an anode consisting essentially of a light metal, a cathode, a separator interposed between the anode and the cathode, an organic electrolyte and a cell case containing the above anode, cathode, separator and organic electrolyte; the anode, cathode and separator being spirally wound so that the anode is positioned on the outer side of the cathode to form an electrode assembly, wherein the outermost end of the cathode is wrapped with an electrically insulating material, wherein the anode has a section provided with an anode current collector in the vicinity of the outermost end thereof, the section being positioned beyond the wrapped outermost end of the cathode in the winding direction of the spiral, and wherein a reaction suppressing layer is present between a cathode section in the vicinity of the outermost end and the anode positioned on the inner side of the above-mentioned cathode section, whereby only the outer side of the cathode section in the vicinity of the outermost end substantially reacts with the anode.
In the non-aqueous electrolyte cell according to the present invention, in the section where the cathode faces the reaction suppressing layer, the cathode reacts with the anode on its outer side in preference to the cathode on its inner side. As a result, at the last stage of discharge, the anode section on the outer side facing the specific section of the cathode is rapidly depleted, and consequently, the anode metal in the inward side from the depleted section is disconnected from the current collector. Since the anode current collector is disposed in the vicinity of outermost end of the anode, the amount of the anode metal remaining in contact with the current collector is very small at the stage where the current collector is disconnected from the anode metal in the inward side, permitting better use of the anode capacity.